The present invention relates to the field of data and/or power transmission. More specifically, it relates to apparatus for transmitting data and/or power from downhole tool strings to stationary equipment, such as surface equipment.
Downhole tool strings, such as drill strings, have become increasingly versatile in the last half century. In addition to traditional oil, gas, and geothermic exploration and production purposes, tubular tool strings are often used for what is known as horizontal directional drilling to install underground power lines, communication lines, water lines, sewer lines, utility lines, and gas lines. This sort of downhole drilling is particularly useful for boring underneath roadways, waterways, populated areas, and environmentally protected areas.
The increased versatility of downhole drilling with tool strings has led to a higher demand for apparatus that are able to transmit a power signal to downhole equipment as well as transmit data and/or power between downhole tools and surface equipment. Hence, several different approaches to solving the problem of transmitting an electrical signal across the joints of a tool string have been developed and are known in the art.
U.S. Pat. Nos. 6,670,880 and 6,717,501 to Hall et al., both of which are incorporated herein by reference for all that they disclose, teach of a system wherein tubular components are coupled at threaded joints and comprises a signal transmission system in the tool string. Other downhole telemetry systems are disclosed in U.S. Pat. No. 6,688,396 to Floerke et al and U.S. Pat. No. 6,641,434 to Boyle et al, which are also herein incorporated by reference for all that they contain.
Optimally, a system for transmitting power or data between surface equipment and downhole tools in a tool string should be transparent to the tool string operator or crew, as time delays introduced by a complicated telemetry system may represent a significant amount of money.
The use of data swivels for transmitting real-time data to stationary equipment has been disclosed in the art. Some examples of Mercury-type rotating electrical contacts that may be used in data swivels are found in U.S. Pat. No. 2,702,890 to Hildebrandt; U.S. Pat. No. 3,021,496 to Kenyon; U.S. Pat. No. 3,022,479 to Rohrbach; and U.S. Pat. No. 3,957,330 to Roscoe et al. Examples of inductive swivels for use in downhole applications are disclosed in U.S. Pat. Nos. 7,098,802 and 7,193,527 both to Hall et al. Each of the above listed patents is herein incorporated by reference.